As 2-cyanoacrylates are instantaneously anionically polymerized to form rigid polymers, they are widely utilized as instantaneous adhesives, rapid-curing fillers and the like in various industries, medical fields, leisure fields and houses. Cured products of 2-cyanoacrylates are generally transparent and colorless and have advantages in that portions subjected to adhesion, filling or surface treatment are inconspicuous and do not spoil appearance.
However, as 2-cyanoacrylates are transparent and colorless even in liquid form during coating and filling, they have disadvantages in terms of handling in that sites which have been coated or filled with them are hard to be distinguished and the amount of coating is difficult to be determined.
Conventionally, various methods have been investigated in order to solve these problems. For example, these methods include a method in which coloring materials are added to 2-cyanoacrylates (U.S. Pat. No. 2,784,127 specification (column 5)) and a method in which anthraquinone-based coloring materials that have good color development properties, are blended with 2-cyanoacrylates (U.S. Pat. No. 3,699,076 specification (columns 3-5 and 8)). In addition, they include a method in which coloring materials having a structure that emits a specific fluorescence are used so as to visually recognize it by irradiation with ultraviolet rays (U.S. Pat. No. 4,405,750 specification (columns 4-5)) and a method in which coloring is carried out by adding salts of basic dyes with various acids (Japanese Patent Laid-Open No. 52-65531 (claims, and page 3)).
When 2-cyanoacrylate-based compositions are used for adhesion, filling, surface treatment or the like, it is of interest whether or not coated adhesives and cured products, particularly their portions or parts that will be shown or exposed after curing can be clearly determined visually (hereinafter referred to as “visibility”), in as much as the present invention focuses on appearance after curing. Namely, for applications in which workability is of interest, it is preferred that 2-cyanoacrylates are colored before curing to an extent that visibility is good. On the other hand, it is preferred that cured products and their exposed parts are inconspicuous, that is, transparent and colorless or nearly colorless, in consideration of appearance after curing.
However, with regard to the incorporation of coloring materials, conventional visible coloring materials improve the visibility during coating, but are still disadvantageous in that they also color cured products and spoil the appearance. Moreover, fluorescent coloring materials express visibility by irradiating them with ultraviolet rays, but have several defects, for example, in that an ultraviolet ray irradiation apparatus is needed and ultraviolet rays may affect human bodies.